Jiang-Fei Xu

Dynamic Covalent Bond Based on Reversible Photo [4 + 4] Cycloaddition of Anthracene for Construction of Double-Dynamic Polymers

Dynamic covalent bonds supplied by reversible anthracene dimerization were combined with pillar[5]arene/imidazole host-guest interactions to construct double-dynamic polymers. Heating such polymers (in solution or as a gel) led to depolymerization by dissociation of either the host-guest complexes alone or the complexes and the anthracene dimers, depending on the extent of heating. The polymers reformed readily upon cooling or irradiation.

Synthesis of a Photoresponsive Cryptand and Its Complexations with Paraquat and 2,7-Diazapyrenium

A McMurry coupling reaction was used for the efficient synthesis of a bis(m-phenylene)-32-crown-10 based cryptand Z-3 with high yield. This photoresponsive cryptand formed host-guest complexes with paraquat derivative 4 and 2,7-diazapyrenium derivative 5. Z-3, and E-3 exhibited similar binding affinity to the small guest 4, while dramatic changes were observed in the binding affinity to the large guest 5.

Supramolecular Hydrogels Fabricated from Supramonomers: A Novel Wound Dressing Material

Daily repeated wound dressing changes will lead to additional trauma to newly formed tissue and prolonging the healing process. In this letter, we designed and fabricated an easily removable wound dressing material. To accomplish this, we first generated cross-linkable supramonomers through host-guest noncovalent interaction, followed by radical copolymerization of acrylamide with supramonomer as cross-linker to fabricate supramolecular hydrogels. Benefiting from the dynamic nature of the supramonomer, the supramolecular hydrogel is able to dissolve upon exposure to memantine, an FDA approved drug, making it easily removed from a wound, representing a promising candidate for the new generation of wound dressing.

Pillar[6]arene Containing Multilayer Films: Reversible Uptake and Release of Guest Molecules with Methyl Viologen Moieties.

Pillar[6]arene-containing multilayer films have been fabricated by alternating deposition of a stoichiometric complex consisting of both pillar[6]arene and methyl viologen with a photoreactive polyelectrolyte, diazoresin (DAR). After photoinduced cross-linking of the multilayer films, the guest molecule, methyl viologen, can be removed. Then, multilayer films with artificial binding sites are fabricated. The films show good properties for molecular uptake and release as well as selectivity for molecules with methyl viologen moieties. It is anticipated that this kind of multilayer films have future applications in the fields of enrichment of molecular dyes and purification of methyl viologen-polluted water.

A Supramolecularly Activated Radical Cation for Accelerated Catalytic Oxidation

Tuning the activity of radicals is crucial for radical reactions and radical-based materials. Herein, we report a supramolecular strategy to accelerate the Fenton reaction through the construction of supramolecularly activated radical cations. As a proof of the concept, cucurbit[7]uril (CB[7]) was introduced, through host-guest interactions, onto each side of a derivative of 1,4-diketopyrrolo[3,4-c]pyrrole (DPP), a model dye for Fenton oxidation. The DPP radical cation, the key intermediate in the oxidation process, was activated by the electrostatically negative carbonyl groups of CB[7]. The activation induced a drastic decrease in the apparent activation energy and greatly increased the reaction rate. This facile supramolecular strategy is a promising method for promoting radical reactions. It may also open up a new route for the catalytic oxidation of organic pollutants for water purification and widen the realm of supramolecular catalysis.

How to Make Weak Noncovalent Interactions Stronger

By employing noncovalent interactions, chemists have constructed a variety of molecular aggregates with well-defined structures and fascinating properties. In fabricating stable and large molecular assemblies, noncovalent interactions with high binding strength are needed. This Concept summarizes some strategies to modify and optimize the structures of building blocks for making weak noncovalent interactions stronger. The strategies include: 1) Preorganization of binding sites; 2) spatial confinement effects; 3) multivalent enhancement; 4) synergistic binding with multiple forces. Examples of the fabrication of supramolecular architectures by utilizing these strategies are presented and discussed. Guidance is offered in the construction and fabrication of stable molecular assemblies and supramolecular materials.

Hydrogen Bonding Directed Self-Assembly of Small-Molecule Amphiphiles in Water

Compounds comprising one or two quadruply hydrogen bonding units, 2-ureido-4[1H]-pyrimidinone (UPy) and tris(tetraethylene glycol monomethyl ether) moieties, were reported to form highly stable hydrogen-bonded assemblies in water. Compound 1, containing one UPy, assembles into vesicles, and compound 2, containing two UPy units, forms micelles. The aggregates disassemble reversibly when the solution pH is raised to 9.0 or above. The results demonstrate the utility of hydrogen bonding to direct the self-assembly of small-molecule building blocks in aqueous media.

Photo-responsive supramolecular polymers synthesized by olefin metathesis polymerization from supramonomers

This communication reports the construction of supramonomers based on the dimerization of styrene terminated ureido-pyrimidinone driven by quadruple hydrogen bonding. The supramolecular polymer was obtained by olefin metathesis of supramonomers. Benefiting from the photo-responsiveness of stilbene units and the dynamic behaviour of double bonds in the presence of ruthenium catalysts, the molecular weight of the supramolecular polymer can be regulated through reversible conformational modulation by UV irradiation and ruthenium catalysts. It is expected that this research will enrich the methodology of fabricating supramolecular polymers with controlled structures.

Controllable supramolecular polymerization through self-sorting of aliphatic and aromatic motifs

Self-sorting is one of the effective strategies to realize control over supramolecular polymerization. In this work, we designed a bifunctional monomer (Np-Cn-Np) bearing an alkyl chain (Cn) and two naphthalene moieties (Np). By mixing the monomer with two kinds of host molecules, the selective recognition between Np and cucurbit[8]uril (CB[8]) can link up the monomer, and the complexation between Cn and cucurbit[7]uril (CB[7]) can construct a rigid linker to promote and control the linear supramolecular polymerization. The self-sorting process was confirmed by 1H NMR and isothermal titration calorimetry. As indicated by analytical ultracentrifugation, the molecular weight of supramolecular polymers can be well tuned from 10 kDa to 50 kDa by tuning the molar ratio of CB[7] to Np-C6-Np. Adjustment of the length of the alkyl chain can influence the degree of polymerization, which was studied through isothermal titration calorimetry and diffusion-ordered NMR spectroscopy. In addition, the kinetics of the supramolecular polymerizations were studied by stopped flow. This line of research will extend the self-sorting strategy to achieve controllable supramolecular polymerization and enrich the field of supramolecular polymers.

Cytotoxicity Regulated by Host–Guest Interactions: A Supramolecular Strategy to Realize Controlled Disguise and Exposure

This work is aimed at providing a supramolecular strategy for tuning the cytotoxicity in chemotherapy. To this end, as a proof of concept, we employed dynamic cucurbit[7]uril(CB[7])-mediated host-guest interaction to control the loading and releasing of dimethyl viologen (MV) as a model antitumor agent. MV has high cytotoxicity to both normal cells and tumor cells without specificity. By encapsulating MV into the hydrophobic cavity of CB[7], the cytotoxicity of MV to normal cells can be significantly decreased. When the host-guest complex of MV-CB[7] is added into tumor cells with overexpressed spermine, the antitumor activity of MV can be recovered in tumor cell environment. There are two reasons behind this effect: on the one hand, spermine has a high affinity to CB[7], leading to releasing of MV from MV-CB[7]; on the other hand, CB[7] can soak up spermine, which is essential for tumor cell growth, therefore decreasing the cell viability furthermore. Then, it is highly anticipated that this kind of supramolecular strategy could apply to clinical antitumor agents and provide a new approach for decreasing the cytotoxicity and increasing the antitumor activity, thus opening horizons of supramolecular chemotherapy.